These pumps will last pretty much forever if you change the oil and rebuild every few years. I am rebuilding 2 E2M5s now but the process is pretty much the same. Here is a great link that I found especially useful for rebuilding the Edwards E2 series.

Special thanks to pcmeiners on eevlog forum for all the below that I copied!

There should be ZERO difference between a rebuilt/overhauled pump and a new one. If there is then it was either rebuilt poorly, or fubar'd to the point of needing hard parts. Edwards is largely overpriced and overhyped. Hell I'm the western edwards authorized service shop and id stick with alcatel/aixden/aligent/varian.